[bryan-harter]

Summary

• Rank spacecraft ephemeris files by numeric OD solution, then ingestion time, independent of database row order.
• Break exact OD/timestamp ties deterministically by filename; keep unnumbered legacy files below numbered solutions.
• Preserve subtype precedence, latest-version-per-file-root behavior, gap filling, and timestamp priority for non-ephemeris kernels.
• Document the selection rules and the production-data validation needed before deployment.

Tests and checks

• pytest tests/lambda_endpoints/test_spice_metakernel_api.py -k ephemeris -q: 38 passed.
• Ruff lint and format checks passed.

Before deployment

The production spice_files selection comparison called for in #1743 remains outstanding: this environment has no production-database access, and no deployment was attempted.

Closes #1743